1. Field of the Invention
The present invention is directed to a new class of photoresists which include hydroxycarboranes. More specifically, the present invention is directed to a photoresist which includes a hydroxycarborane additive or pendent group on a polymeric backbone.
2. Background of the Prior Art
Advances in the semiconductor arts are driven by many technological developments. Among these are process improvements which allow semiconductor chips to be lithographically patterned in ever smaller geometries. These improvements, in turn, have been accomplished in the past by continually reducing the wavelength of the imaging radiation from the visible light range, i.e. 436 nm, down to the presently employed ultraviolet (UV) range, i.e. 248 to 365 nm. Indeed, present day lithography is predicated on utilizing imaging radiation at a UV wavelength of 193 nm. Future wavelength imaging is contemplated to employ lasers utilizing a UV wavelength of 157 nm. Looking out further into the future, imaging radiation having a wavelength in the extreme UV range of 13 nm has been proposed.
As photoresist transparency decreases to these short wavelengths, accompanied by shrinkage in device geometries to below 100 nm, there is an increased need in the art for thin film imaging approaches to accommodate these reduced wavelengths.
An accepted means for providing thin film imaging is the utilization of photoresists which incorporate silicon in an oxygen-reactive ion etching (O2-RIE) process. Such means employ the bilayer process or the top surface imaging process. Both of these methods rely on differences between oxygen plasma etch rates of polymers that contain elements forming refractory oxides, i.e. silicon oxide, and simple organic polymers comprised only of elements forming volatile oxides.
Although the use of silicon-containing photoresists in this application represent a significant advance in the art, such photoresists suffer from a major deficiency, the improvement of which has been long sought by those skilled in the art. That is, as those skilled in the art are aware, silicon-containing photoresists are not sufficiently acidic to provide optimum removal of exposed portions of the photoresist during the lithographic procedure. Indeed, phenolic materials, which are used in higher wavelength imaging operations, provide a standard upon which other photoresist materials are judged in regard to photoresist removal based on photoresist acidity. However, phenolic-based photoresists are not optically transparent in the UV wavelength range. Thus, phenolic materials are not employed in state of the art thin film UV wavelength range lithographic applications.
It is thus apparent that a new class of photoresists suitable for utilization in O2-RIE thin film imaging lithography represents a pressing need in the art.
Hydroxycarboranes have been described in the art. I. Zharov et al., Inorganic Chem. 36, No. 36, 6033-6038 (1997) describes such a class of hydroxycarboranes. That technical article, however, provides no disclosure or suggest of utilizing the compounds described therein as photoresists, let alone disclosing or suggesting photoresists which include a polymeric backbone to which hydroxycarboranes are attached as an additive or pendent group.
It has now been discovered that a new class of photoresists suitable for utilization in O2-RIE provide both excellent transparency in the ultraviolet light wavelength range and excellent processability in thin film imaging lithography in production of semiconductor devices and the like.
In accordance with the present invention a photoresist composition is provided. The photoresist composition includes an acid labile polymer, a hydroxycarborane monomeric dissolution modifier and a photoacid generator. Alternatively, the photoresist composition includes a hydroxycarborane as a pendent group on a polymeric backbone and a photoacid generator.
In further accordance with the present invention a process of bilayer thin-film imaging lithography is provided in which a hydroxycarborane photoresist is utilized.